The present invention generally relates to plastic bags and, more particularly, to a plastic bag capable of standing up by itself before, during and after being filled and to a method making the bag.
So-called stand-up, free-standing or self-standing plastic bags are well-known in the prior art. Representative of the prior art are the plastic bags disclosed in U.S. Pat. Nos. to Knuetter (2,265,075), Doyen et al (3,380,646), Kugler (3,437,258), Michel (3,715,074) and Bustin (4,353,497). Also, well-known in the prior art are plastic bags incorporating a zipper-type closure device along the top opening or mouth of the bags. Representative of the prior art are the plastic bags disclosed in a U.S. Pat. No. to Ausnit (4,601,694) and a U.K. Patent Application to Kirkpatrick (2,047,199). Further, U.S. Pat. Nos. to Kan (3,980,225 and 4,055,109) disclose a self-standing plastic bag which also incorporates a zipper-type closure device along its mouth.
Market research has shown that consumers greatly desire a stand-up, reclosable plastic bag because of the convenience of filling and storing highly liquid foods and of microwave heating of foods directly in the bag. Some known stand-up bags attempt to provide the stand-up capability merely by use of a simple bottom gusset alone or supplemented with seals added in the gusset structure. A simple bottom gusset sealed at its sides does not provide a normal consumer plastic bag with a sufficient stand-up feature. Such plastic bag typically made from polyethylene film, for example of under 1.0 mil thickness, is too limp to stand up from the gusseted bottom.
Other plastic films of greater thickness and higher modulus can be fabricated into a bag that will stand up from a simple bottom gusset. One plastic bag currently available uses a very deep bottom gusset design to provide certain advantages in food storage and microwave heating, but some difficulty has been experienced in filling and emptying this bag. The bag does not stand up easily when empty, and the zipper-type closure is difficult to maintain open when filling and emptying this bag. Other currently-available stand-up bags seal the bottom gusset into a stand-up base that is much more stable than the simple bottom gusset. The self-standing bag of the above-cited U.S. patents to Kan is an example of a bag having such stand-up base.
It is perceived that additional improvements need to be made before consumers will be provided with a stand-up reclosable plastic bag that fully meets their needs. These improvements must relate to the provision of a bag with a stronger, sturdier and more stable stand-up base, one which will faithfully support the bag when empty as well as during and after filling, and a bag with a more reliable, leak-proof side seam. Aslo, the improvements must allow a simpler and less costly method of making the bag.